Method of forming a positive image through infrared exposure utilizing diazonaphthoquinone imaging composition

ABSTRACT

An infrared imaging composition contains two essential components, namely an infrared absorbing compound, and a phenolic resin that is either mixed or reacted with an o-diazonaphthoquinone derivative. These compositions are useful in positive-working elements such as lithographic printing plates that can be adapted to direct-to-plate imaging procedures. The weight ratio of infrared radiation absorbing compound to diazonaphthoquinone moiety is less than 1:14.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of Ser. No. 08/723,335, filedSep. 30, 1996, now U.S. Pat. No. 5,705,308.

FIELD OF THE INVENTION

This invention relates to a photosensitive composition andpositive-working element that are sensitive to infrared radiation. Inparticular, this invention relates to positive-working lithographicprinting plates.

BACKGROUND OF THE INVENTION

The art of lithographic printing is based up on the immiscibility of oiland water, wherein the oily material or ink is preferentially retainedby the image area and the water or fountain solution is preferentiallyretained by the non-image area. When a suitably prepared surface ismoistened with water and an ink is then applied, the background ornon-image areas retain the water and repel the ink while the image areasaccept the ink and repel the water. The ink on the image areas is thentransferred to the surface of a material upon which the image is to bereproduced, such as paper, cloth and other materials. Commonly, the inkis transferred to an intermediate material called the blanket which inturn transfers the ink to the surface of the material upon which theimage is to be reproduced.

A widely used type of lithographic printing plate has a light-sensitivecoating applied to an aluminum base support. The coating may respond tolight by having the portion that is exposed become soluble so that it isremoved in the developing process. Such a plate is referred to in theart as a positive-working printing plate. Conversely, when that portionof the coating that is exposed becomes hardened, the plate is referredto as a negative-working plate. In both instances, the image areasremaining are ink-receptive or oleophilic and the non-image areas orbackground are water-receptive or hydrophilic. The differentiationbetween image and non-image areas is made in the exposure process wherea film is applied to the plate with a vacuum to insure good contact. Theplate is then exposed to a light source, a portion of which is composedof UV radiation. In the instance of negative-working plates, the areason the film corresponding to the image areas are clear, allowing lightto harden the image area coating, while the areas on the filmcorresponding to the non-image areas are black, preventing the lighthardening process, so the areas not struck by light can be removedduring development. The light-hardened surfaces of a negative-workingplate are therefore oleophilic and will accept ink while the non-imageareas that have had the coating removed through the action of adeveloper are desensitized and are therefore hydrophilic.

Various useful printing plates that can be either negative-working orpositive-working are described, for example, in GB 2,082,339 (HorsellGraphic Industries), and U.S. Pat. No. 4,927,741 (Garth et al), both ofwhich describe imaging layers containing an o-diazonaphthoquinone and aresole resin, and optionally a novolac resin. Another plate that can besimilarly used is described in U.S. Pat. No. 4,708,925 (Newman) whereinthe imaging layer comprises a phenolic resin and a radiation-sensitiveonium salt. This imaging composition can also be used for thepreparation of a direct laser addressable printing plate, that isimaging without the use of a photographic transparency.

Direct digital imaging of offset printing plates is a technology thathas assumed importance to the printing industry. The first commerciallysuccessful workings of such technology made use of visiblelight-emitting lasers, specifically argon-ion and frequency doubledNd:YAG lasers. Printing plates with high photosensitivities are requiredto achieve acceptable through-put levels using plate-setters equippedwith practical visible-light laser sources. Inferior shelf-life, loss inresolution and the inconvenience of handling materials under dimlighting are trade-offs that generally accompany imaging systemsexhibiting sufficiently high photosensitivities.

Advances in solid-state laser technology have made high-powered diodelasers attractive light sources for plate-setters. Currently, at leasttwo printing plate technologies have been introduced that can be imagedwith laser diodes emitting in the infrared regions, specifically atabout 830 nm. One of these is described in EP 573,091 (Agfa) and inseveral patents and published applications assigned to Presstek, Inc forexample, U.S. Pat. No. 5,353,705 (Lewis et al), U.S. Pat. No. 5,351,617(Williams et al), U.S. Pat. No. 5,379,698 (Nowak et al), U.S. Pat. No.5,385,092 (Lewis et al) and U.S. Pat. No. 5,339,737 (Lewis et al)!. Thistechnology relies upon ablation to physically remove the imaging layerfrom the printing plate. Ablation requires high laser fluences,resulting in lower through-puts and problems with debris after imaging.

A higher speed and cleaner technology is described, for example, in U.S.Pat. No. 5,340,699 (Haley et al), U.S. Pat. No. 5,372,907 (Haley et al),U.S. Pat. No. 5,466,557 (Haley et al) and EP-A-0 672 954 (Eastman Kodak)which uses near-infrared energy to produce acids in an imagewisefashion. These acids catalyze crosslinking of the coating in apost-exposure heating step. Precise temperature control is required inthe heating step. The imaging layers in the plates of U.S. Pat. No.5,372,907 (noted above) comprise a resole resin, a novolac resin, alatent Bronsted acid and an infrared absorbing compound. Otheradditives, such as various photosensitizers, may also be included.

DE-4,426,820 (Fuji) describes printing plates that can be imaged in thenear infrared at moderate power levels with relatively simple processingrequirements. In one embodiment, the printing plate has at least twolayers: an imaging layer containing an o-diazonaphthoquinone compoundand an infrared absorbing compound, and a protective overcoat containinga water-soluble polymer or silicone polymer. Other plates have a singlelayer. In all cases, the plates are floodwise exposed with ultravioletlight to convert the o-diazonaphthoquinone to an indenecarboxylic acid,which is then imagewise decarboxylated by means of heat transferred fromthe infrared absorbing material. Development with an alkaline solutionresults in removal of areas not subjected to thermal decarboxylation.The pre-imaging floodwise exposure step, however, is awkward in that itprecludes the direct loading of the printing plates into plate-setters.

Thus, there is a need for positive-working printing plates that can beeasily imaged in the near infrared at moderate power levels and that canbe directly processed after imaging.

SUMMARY OF THE INVENTION

The problems noted above with known photosensitive compositions andprinting plates are overcome with a positive-working imaging compositionconsisting essentially of:

a) (i) a mixture of a phenolic resin and an o-diazonaphthoquinonederivative,

(ii) a reaction product of a phenolic resin and an o-diazonaphthoquinonereactive derivative, or

(iii) a mixture of (i) and (ii) and

b) a compound that absorbs infrared radiation at a maximum absorptionwavelength greater than 750 nm,

wherein the weight ratio of b) to the diazonaphthoquinone of a) is lessthan 1:14.

This invention also provides an element consisting essentially of asupport having thereon a positive-working imaging layer consistingessentially of the imaging composition described above.

This invention also provides a method of creating a positive imageconsisting essentially of the steps of:

A) providing an element as described above,

B) without prior or simultaneous floodwise exposure, imagewise exposingthe element with an infrared radiation emitting laser, and

C) contacting the element with an aqueous developing solution to removethe image areas.

The imaging composition and element of this invention are useful forproviding high quality positive images using moderately powered lasers.This makes the element much more convenient to use in plate-setters. Theelement of this invention also does not need a protective overcoatthereby eliminating the materials and coating step required for suchlayers. Moreover, such elements are imagewise exposed without any prioror simultaneous floodwise exposure to UV or other actinic radiation.

Since the elements of this invention are infrared sensitive, digitalimaging information can be conveniently utilized to form continuous orhalftone images using the moderately powered laser diodes.

DETAILED DESCRIPTION OF THE INVENTION

As noted above, the positive-working imaging composition of thisinvention contains only two essential components a) and b):

a) either

(i) a mixture of a phenolic resin and an o-diazonaphthoquinonederivative,

(ii) a reaction product of a phenolic resin and an o-diazonaphthoquinonereactive derivative, or

(iii) a mixture of (i) and (ii), and

b) a compound that absorbs infrared radiation at a maximum absorptionwavelength greater than 750 nm.

The resins useful in the practice of this invention to form a reactionproduct with an o-diazonaphthoquinone reactive derivative can be anytype of resin that has a suitable reactive group for participating insuch a reaction. For example, such resins can have a reactive hydroxygroup. The phenolic resins defined below are most preferred, but otherresins include copolymers of acrylates and methacrylates withhydroxy-containing acrylates or methacrylates, as described for examplein U.S. Pat. No. 3,859,099 (Petropoulos et al), for example, a copolymerof hydroxyethyl methacrylate and methyl methacrylate.

The phenolic resins useful herein are light-stable, water-insoluble,alkali-soluble film-forming resins that have a multiplicity of hydroxygroups either on the backbone of the resin or on pendant groups. Theresins typically have a molecular weight of at least 350, and preferablyof at least 1000, as determined by gel permeation chromatography. Anupper limit of the molecular weight would be readily apparent to oneskilled in the art, but practically it is about 100,000. The resins alsogenerally have a pKa of not more than 11 and as low as 7.

As used herein, the term "phenolic resin" includes, but is not limitedto, what are known as novolac resins, resole resins and polyvinylcompounds having phenolic hydroxy groups. Novolac resins are preferred.

Novolac resins are generally polymers that are produced by thecondensation reaction of phenols and an aldehyde, such as formaldehyde,or aldehyde-releasing compound capable of undergoing phenol-aldehydecondensation, in the presence of an acid catalyst. Typical novolacresins include, but are not limited to, phenol-formaldehyde resin,cresol-formaldehyde resin, phenol-cresol-formaldehyde resin,p-t-butylphenol-formaldehyde resin, and pyrogallol-acetone resins. Suchcompounds are well known and described for example in U.S. Pat. No.4,308,368 (Kubo et al), U.S. Pat. No. 4,845,008 (Nishioka et al), U.S.Pat. No. 5,437,952 (Hirai et al) and U.S. Pat. No. 5,491,046 (DeBoer etal), U.S. Pat. No. 5,143,816 (Mizutani et al) and GB 1,546,633 (EastmanKodak). A particularly useful novolac resin is prepared by reactingm-cresol or phenol with formaldehyde using conventional conditions.

Another useful phenolic resin is what is known as a "resole resin" thatis a condensation product of bis-phenol A and formaldehyde. One suchresin is commercially available as UCAR phenolic resin BKS-5928 fromGeorgia Pacific Corporation.

Still another useful phenolic resin is a polyvinyl compound havingphenolic hydroxyl groups. Such compounds include, but are not limitedto, polyhydroxystyrenes and copolymers containing recurring units of ahydroxystyrene, and polymers and copolymers containing recurring unitsof halogenated hydroxystyrenes. Such polymers are described for examplein U.S. Pat. No. 4,845,008 (noted above). Other hydroxy-containingpolyvinyl compounds are described in U.S. Pat. No. 4,306,010 (Uehara etal) and U.S. Pat. No. 4,306,011 (Uehara et al) which are prepared byreacting a polyhydric alcohol and an aldehyde or ketone, several ofwhich are described in the patents. Still other useful phenolic resinsare described in U.S. Pat. No. 5,368,977 (Yoda et al).

A mixture of the resins described above can be used, but preferably, asingle novolac resin is present in the imaging composition of thisinvention.

When the composition of this invention is formulated as a coatingcomposition in suitable coating solvents, the resin is present in anamount of at least 0.5 weight percent. Preferably, it is present in anamount of from about 1 to about 10 weight percent.

In the dried imaging layer of the element of this invention, the resinis the predominant material. Generally, it comprises at least 25 weightpercent of the layer, and more preferably, it is from about 60 to about90 weight percent of the dried layer.

In one embodiment of this invention, a phenolic resin is present inadmixture with an o-diazonaphthoquinone derivative. Such compoundscomprise an o-diazonaphthoquinone moiety or group attached to aballasting moiety that has a molecular weight of at least 15, but lessthan 5000.

The o-diazonaphthoquinone derivatives have at least oneo-diazonaphthoquinone moiety or group in the molecule, and which is mademore soluble in an alkali solution upon irradiation with actinic light.Such derivatives are prepared from compounds that are well known in theart, including those described, for example in Kosar, Light-SensitiveSystem, John Wiley & Sons Inc., 1965, such as esters or amides with asuitable aromatic polyhydroxy compound or amine. Examples are esters of2-diazo-1,2-dihydro-1-oxonaphthalenesulfonic acid or carboxylic acidchlorides.

Useful derivatives include, but are not limited to:

2,4-bis(2-diazo-1,2-dihydro-1-oxo-5-naphthalenesulfonyloxy)benzophenone,

2-diazo-1,2-dihydro-1-oxo-5-naphthalenesulfonyloxy-2,2-bishydroxyphenylpropane monoester,

the hexahydroxybenzophenone hexaester of2-diazo-1,2-dihydro-1-oxo-5-naphthalenesulfonic acid,

2,2'-bis(2-diazo-1,2-dihydro-1-oxo-5-naphthalenesulfonyloxy)biphenyl,

2,2',4,4'-tetrakis(2-diazo-1,2-dihydro-1-oxo-5-naphthalenesulfonyloxy)biphenyl,

2,3,4-tris(2-diazo-1,2-dihydro-1-oxo-5-naphthalenesulfonyloxy)benzophenone,

2,4-bis(2-diazo-1,2-dihydro-1-oxo-4-naphthalenesulfonyloxy)benzophenone,

2-diazo-1,2-dihydro-1-oxo-4-naphthalenesulfonyloxy-2,2-bishydroxyphenylpropane monoester,

the hexahydroxybenzophenone hexaester of2-diazo-1,2-dihydro-1-oxo-4-naphthalenesulfonic acid,

2,2'-bis(2-diazo-1,2-dihydro-1-oxo-4-naphthalenesulfonyloxy)biphenyl,

2,2',4,4'-tetrakis(2-diazo-1,2-dihydro-1-oxo-4-naphthalenesulfonyloxy)biphenyl,

2,3,4-tris(2-diazo-1,2-dihydro-1-oxo-4-naphthalenesulfonyloxy)benzophenone,and

others known in the art, for example described in U.S. Pat. No.5,143,816 (noted above).

The dry weight ratio of phenolic resin to o-diazonaphthoquinonederivative in this embodiment is generally at least 0.5:1, and a weightratio of from about 2:1 to about 6:1 is preferred.

In another and preferred embodiment of this invention, a reactionproduct of a resin (as described above) and an o-diazonaphthoquinonereactive derivative is used in the imaging composition. Such aderivative has a functional group (such as chloride or reactive imidegroup) that can react with a suitable reactive group (for example, ahydroxy group) of the resin (such as a phenolic resin) and therebybecome part of the resin, rendering the resin sensitive to actinicradiation. The reactive group can be in the 4- or 5-position of theo-diazonaphthoquinone molecule.

Representative reactive compounds include sulfonic and carboxylic acid,ester or amide derivatives of the o-diazonaphthoquinone moiety.Preferred compounds are the sulfonyl chloride or esters, and thesulfonyl chlorides are most preferred. Reactions with the phenolicresins are well known in the art, being described for example in GB1,546,633 (noted above), U.S. Pat. No. 4,308,368 (noted above) and U.S.Pat. No. 5,145,763 (Bassett et al).

The amount of o-diazonaphthoquinone moiety in the dried imagingcomposition is generally at least 5 weight percent, and more preferablyfrom about 15 to about 40 weight percent.

The second essential component of the imaging composition of thisinvention is an infrared radiation absorbing compound (or IR absorbingcompound), or mixture thereof. Such compounds typically have a maximumabsorption wavelength (λ_(max)) in the region of at least 750 nm, thatis in the infrared region and near infrared of the spectrum, and moreparticularly, from about 800 to about 1100 nm. Thus, such compounds arenot intended to include broad band absorbers that may minimally absorbin the near infrared or infrared regions but whose maximum absorptionwavelengths are in the visible or UV regions (that is, below about 750nm). The compounds can be dyes or pigments, and a wide range ofcompounds are well known in the art (including U.S. Pat. No. 4,912,083,U.S. Pat. No. 4,942,141, U.S. Pat. No. 4,948,776, U.S. Pat. No.4,948,777, U.S. Pat. No. 4,948,778, U.S. Pat. No. 4,950,639, U.S. Pat.No. 4,950,640, U.S. Pat. No. 4,952,552, U.S. Pat. No. 4,973,572, U.S.Pat. No. 5,036,040 and U.S. Pat. No. 5,166,024). Classes of materialsthat are useful include, but are not limited to, squarylium, croconate,cyanine (including phthalocyanine), merocyanine,chalcogenopyryloarylidene, oxyindolizine, quinoid, indolizine, pyryliumand metal dithiolene dyes or pigments. Other useful classes includethiazine, azulenium and xanthene dyes. Particularly useful infraredabsorbing dyes are of the cyanine class.

The amount of infrared absorbing compound in the dried imaging layer isgenerally sufficient to provide an optical density of at least 0.5 inthe layer, and preferably, an optical density of from about 1 to about3. This range would accommodate a wide variety of compounds havingvastly different extinction coefficients. Generally, this is at least 1weight percent, and preferably from about 5 to about 25 weight percent.

It is critical that the dry weight ratio of infrared radiation absorbingcompound to diazonaphthoquinone moiety (whether in admixture or areaction product) be less than 1:14, and preferably, it is from about1:50 to about 1:330, for the composition of this invention to bepositive-working.

Optional, non-essential components of the imaging composition includecolorants, sensitizers, stabilizers, exposure indicators and surfactantsin conventional amounts.

Another optional component of the imaging composition is one or morenon-photosensitive "dissolution inhibitor compounds". Such compoundshave polar functionality that serve as acceptor sites for hydrogenbonding with hydroxy groups on aromatic rings. The acceptor sites areatoms with high electron density, preferably selected fromelectronegative first row elements. Useful polar groups include ketogroups and vinylogous esters. Other groups may also be useful, such assulfones, sulfoxides, thiones, phosphine oxides, nitriles, imides,amides, thiols, ethers, alcohols, ureas as well as nitroso, azo, azoxy,nitro and halo groups. In general, it is desired that such compoundshave an "inhibition factor" of at least 0.5, and preferably at least 5.Inhibition factors for given compounds can be readily measured using theprocedure described by Shih et al, Macromolecules, Vol. 27, p. 3330(1994). The inhibition factor is the slope of the line obtained byplotting the log of the development rate as a function of inhibitorconcentration in the phenolic resin coating. Development rates areconveniently measured by laser interferometry, as described byMeyerhofer in IEEE Trans. Electron Devices, ED-27, 921 (1980).

Representative compounds having the desired properties include aromaticketones including, but not limited to, xanthone, flavanone, flavone,2,3-diphenyl-1-indenone, 1'-(2'-acetonaphthonyl)benzoate, α- andβ-naphthoflavone, 2,6-diphenyl-4H-pyran-4-one and2,6-diphenyl-4H-thiopyran-4-one. α-Naphthoflavone,2,6-diphenyl-4H-pyran-4-one and 2,6-diphenyl-4H-thiopyran-4-one arepreferred.

The dissolution inhibitors are not themselves actually sensitive tonear-IR radiation. Their dissolution inhibition abilities are presumablyaltered by the localized heating that results from irradiation of the IRabsorbing compound. Thus, by "non-photosensitive" is meant that thesecompounds are not significantly sensitive to actinic radiation having awavelength above 400 nm, and preferably above 300 nm.

The amount of one or more such compounds in the imaging composition ofthis invention can vary widely, but generally it is at least about 1weight percent, based on the total dry composition weight.

Obviously, the imaging composition is coated out of one or more suitableorganic solvents that have no effect on the sensitivity of thecomposition. Various solvents for this purpose are well known, butacetone and 1-methoxy-2-propanol are preferred. The essential componentsof the composition are dissolved in the solvents in suitableproportions.

Suitable conditions for drying the composition involve heating for aperiod of time of from about 0.5 to about 5 minutes at a temperature inthe range of from about 20° to about 150° C.

To form an element of this invention, the imaging composition is applied(usually by coating techniques) onto a suitable support, such as ametal, polymeric film, ceramics or polymeric-coated paper usingconventional procedures and equipment. Suitable metals include aluminum,zinc or steel, but preferably, the metal is aluminum. A most preferredsupport is an electrochemically grained and sulfuric acid anodizedaluminum sheet that has been further treated with anacrylamide-vinylphosphonic acid copolymer according to the teaching inU.S. Pat. No. 5,368,974. Such elements are generally known aslithographic printing plates, but other useful elements include printedcircuit boards.

The thickness of the resulting imaging layer, after drying, on thesupport can vary widely, but typically it is in the range of from about0.5 to about 2 μm, and preferably from about 1 to about 1.5 μm.

No other essential layers are provided on the element of this invention.In particular, there is no protective or other type of layer over theimaging layer which is the outermost layer. Optional, but not preferredsubbing or antihalation layers can be disposed under the imaging layer,or on the backside of the support (such as when the support is atransparent polymeric film).

The elements of this invention are uniquely adapted for"direct-to-plate" imaging applications. Such systems utilize digitizedimage formation, as stored on a computer disk, compact disk, computertape or other digital information storage media, or information that canbe provided directly from a scanner, that is intended to be printed. Thebits of information in a digitized record correspond to the imageelements or pixels of the image to be printed. This pixel record is usedto control the exposure device, that is a modulated laser beam. Theposition of the laser beam can be controlled using any suitable meansknown in the art, and turned on and off in correspondence with pixels tobe printed. The exposing beam is focused onto the unexposed element ofthis invention. Thus, no exposed and processed films are needed forimaging of the elements, as in the conventional lithographic imagingprocesses.

Laser imaging can be carried out using any moderate or high-intensitylaser diode writing device. Specifically, a laser printing apparatus isprovided that includes a mechanism for scanning the write beam acrossthe element to generate an image without ablation. The intensity of thewrite beam generated at the laser diode source at the element is atleast 10 milliwatts/μm² (preferably from 10-1000 milliwatts/μm²). Duringoperation, the element to be exposed is placed in the retainingmechanism of the writing device and the write beam is scanned across theelement to generate an image.

Following laser imaging, the printing plate of this invention is thendeveloped in an alkaline developer solution until the image areas areremoved to provide the desired positive image. Development can becarried out under conventional conditions for from about 30 to about 120seconds. One useful aqueous alkaline developer solution is a silicatesolution containing an alkali metal silicate or metasilicate. Such adeveloper solution can be obtained from Eastman Kodak Company as KODAKPRODUCTION SERIES Machine Developer/Positive.

After development, the element is usually treated with a finisher suchas gum arabic. However, after imaging, the plate is subjected to noother essential steps, except development. Thus, no post-imaging bakestep is carried out, nor is floodwise exposure needed before or afterimaging. A post-development baking step can be used, if desired, toincrease run length of the plate.

The following examples are provided to illustrate the practice of thisinvention, and not to limit it in any manner. Unless otherwise noted,all percentages are by weight.

EXAMPLE 1

A positive-working imaging coating formulation was prepared as follows:

    ______________________________________    COMPONENT             GRAMS    ______________________________________    Cresol-formaldehyde novolac resin                          42.273    Diester of 2-diazo-1,2-dihydro-1-oxo-5-                          7.128    naphthalenesulfonate and 2,3,4-    trihydroxybenzophenone    IR absorbing dye*     0.599    1-Methoxy-2-propanol solvent                          950    ______________________________________     *IR dye is     2(2-(2-chloro-3-((1,3-dihydro-1,1,3-trimethyl-2H-benz(e)indol-2-ylidene)e    hylidene)-1-cyclohexen-1-yl)ethenyl)-1,1,3-trimethyl-III-benz(e)indolium,     salt with 4methylbenzenesulfonic acid.

This formulation was applied to give a dry coating weight of about 120g/m² onto electrochemically grained and sulfuric acid anodized aluminumsheets that had been further treated with an acrylamide-vinylphosphonicacid copolymer (according to U.S. Pat. No. 5,368,974, noted above) toform an unexposed lithographic printing plate.

The plate was imaged with a 500 milliwatt diode laser emitting amodulated pulse centered at 830 nm. The plate was then processed withKODAK PRODUCTION SERIES Machine Developer/Positive to provide a highresolution positive image.

EXAMPLE 2

A second imaging coating formulation of this invention was preparedusing a cresol-formaldehyde novolac resin (purchased from SchenectadyChemical Company) derivatized (at 3%) with2-diazo-1,2-dihydro-1-oxo-5-naphthalenesulfonyl chloride (45.259 gramsof derivatized resin), the IR absorbing dye of Example 1 (0.626 grams),diester of 2-diazo-1,2-dihydro-1-oxo-5-naphthalenesulfonyloxy and2,3,4-trihydroxybenzophenone (4.115 grams)and 1-methoxy-2-propanolsolvent (950 grams).

This formulation was used to prepare a lithographic printing plate thatwas imaged and processed as described in Example 1 to provide a highresolution positive image.

EXAMPLE 3

Another imaging coating formulation of this invention was prepared usinga cresol-formaldehyde novolac resin (purchased from Schenectady ChemicalCompany) derivatized (at 6%) with2-diazo-1,2-dihydro-1-oxo-5-naphthalenesulfonyl chloride (49.374 gramsof derivatized resin), the IR absorbing dye of Example 1 (0.626 grams),diester of 2-diazo-1,2-dihydro-1-oxo-5-naphthalenesulfonyloxy and2,3,4-trihydroxybenzophenone (4.115 grams) and 1-methoxy-2-propanolsolvent (950 grams).

This formulation was used to prepare a lithographic printing plate thatwas imaged and processed as described in Example 1 to provide a highresolution positive image.

EXAMPLE 4

A similar imaging coating formulation of this invention was preparedusing a cresol-formaldehyde novolac resin (purchased from SchenectadyChemical Co.) derivatized (3%) with2-diazo-1,2-dihydro-1-oxo-4-naphthalenesulfonyl chloride (45.3 grams ofderivatized resin), the IR absorbing dye of Example 1 (0.626 grams), and1-methoxy-2-propanol solvent (950 grams).

This formulation was used to prepare a lithographic printing plate thatwas imaged and processed as described in Example 1 to provide a highresolution positive image.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

We claim:
 1. A method of providing forming a positive image, the methodcomprising the steps of:A) without a prior or a simultaneous floodwiseexposure, imagewise exposing with infrared radiation an imaging layer ofan imaging element, and forming image areas in said imaging layer; andB) contacting said element with an aqueous developing solution andremoving said image areas of said imaging layer;wherein: said imagingelement comprises a support having thereon said imaging layer; saidimaging layer comprises:a) (i) a mixture of a phenolic resin and ano-diazonaphthoguinone derivative,(ii) a reaction product of a phenolicresin and an o-diazonaphthoguinone reactive derivative, or (iii) amixture of (i) and (ii); and b) a compound that absorbs infraredradiation, said compound having a maximum absorption wavelength greaterthan 750 nm; the dry weight ratio of said infrared absorbing compound b)to the o-diazonaphthoguinone moiety in said mixture (i) and in saidreaction product (ii) is less than 1:14; and said imaging layer is theoutermost layer of said element.
 2. The method of claim 1 in which thereis no floodwise exposure between step A) and step B).
 3. The method ofclaim 2 in which component a) is reaction product (ii).
 4. The method ofclaim 3 in which the phenolic resin is a novolac resin.
 5. The method ofclaim 2 in which the ratio is from about 1:50 to about 1:330.
 6. Themethod of claim 2 in which the imaging layer additionally comprises anon-photosensitive dissolution inhibitor compound having an inhibitionfactor of at least 0.5.
 7. The method of claim 2 in which saido-diazonaphthoquinone reactive derivative is a sulfonic acid orcarboxylic acid ester of o-diazonaphthoquinone.
 8. The method of claim 7in which component a) is reaction product (ii) and in which the phenolicresin is a novolac resin.
 9. The method of claim 2 in which saido-diazonaphthoquinone derivative is2,4-bis(2-diazo-1,2-dihydro-1-oxo-5-naphthalenesulfonyloxy)benzophenone,2-diazo-1,2-dihydro-1-oxo-5-naphthalenesulfonyloxy-2,2-bis(hydroxyphenyl)propanemonoester, the hexahydroxybenzophenone hexaester of2-diazo-1,2-dihydro-1-oxo-5-naphthalenesulfonic acid,2,2'-bis(2-diazo-1,2-dihydro-1-oxo-5-naphthalenesulfonyloxy)biphenyl,2,2'4,4'-tetrakis(2-diazo-1,2-dihydro-1-oxo-5-naphthalenesulfonyloxy)biphenyl,2,3,4-tris(2-diazo-1,2-dihydro-1-oxo-5-naphthalenesulfonyloxy)-benzophenone,2,4-bis(2-diazo-1,2-dihydro-1-oxo-4-naphthalene-sulfonyloxy)benzophenone,2-diazo-1,2-dihydro-1-oxo-4-naphthalenesulfonyloxy-2,2-bishydroxyphenylpropanemonoester, the hexahydroxybenzophenone hexaester of2-diazo-1,2-dihydro-1-oxo-4-naphthalenesulfonic acid,2,2'-bis(2-diazo-1,2-dihydro-1-oxo-4-naphthalenesulfonyloxy)biphenyl,2,2',4,4'-tetrakis(2-diazo-1,2-dihydro-1-oxo-4-naphthalenesulfonyloxy)biphenyl,or2,3,4-tris(2-diazo-1,2-dihydro-1-oxo-4-naphthalenesulfonyloxy)benzophenone10. The method of claim 2 in which said infrared radiation absorbingcompound is (i) a squarylium, croconate, cyanine, merocyanine,indolizine, pyrylium or metal dithiolene dye or (ii) a pigment thatabsorbs infrared radiation at a wavelength of from about 800 to about1100 nm.
 11. The method of claim 10 in which component a) is reactionproduct (ii), the phenolic resin is a novolac resin, and theo-diazonaphthoquinone reactive derivative is a sulfonic acid orcarboxylic acid ester of o-diazonaphthoquinone; in which the infraredradiation absorbing compound is present in an amount sufficient toprovide an optical density of at least 0.5; and in which the ratio isfrom about 1:50 to about 1:330.
 12. The method of claim 11 in which theimaging layer additionally comprises a non-photosensitive dissolutioninhibitor compound having an inhibition factor of at least 0.5.
 13. Themethod of claim 11 in which said infrared radiation absorbing compoundis present in an amount sufficient to provide an optical density of fromabout 1 to about
 3. 14. The method of claim 2 wherein said support is apolyester film or a sheet of grained and anodized aluminum.
 15. A methodof forming a positive image, the method comprising the steps of:A)without a prior or simultaneous floodwise exposure, imagewise exposingwith infrared radiation an imaging layer of an imaging element, andforming image areas in said imaging layer; and B) contacting saidelement with an aqueous developing solution and removing said imageareas of said imaging layer;wherein: said imaging element comprises of asupport having thereon said imaging layer; said imaging layer consistsessentially of:a) (i) a mixture of a phenolic resin and ano-diazonaphthoquinone derivative,(ii) a reaction product of a phenolicresin and an o-diazonaphthoquinone reactive derivative, or (iii) amixture of (i) and (ii); and b) a compound that absorbs infraredradiation, said compound having a maximum absorption wavelength greaterthan 750 nm; c) optionally, a non-photosensitive dissolution inhibitorcompound having an inhibition factor of at least 0.5; and d) optionally,one or more components selected from the group consisting of colorants,sensitizers, stabilizers, exposure indicators, and surfactants; saidimaging layer is the outermost layer of said element; the dry weightratio of said infrared absorbing compound b) to theo-diazonaphthoquinone moiety in said mixture (i) and in said reactionproduct (ii) is less than 1:14; and there is no floodwise exposurebetween step A) and step B).
 16. The method of claim 15 in which theratio is from about 1:50 to about 1:330.
 17. The method of claim 16 inwhich component a) is reaction product (ii), the phenolic resin is anovolac resin, and the o-diazonaphthoquinone reactive derivative is asulfonic acid or carboxylic acid ester of o-diazonaphthoquinone; inwhich the infrared radiation absorbing compound is present in an amountsufficient to provide an optical density of at least 0.5; and in whichthe ratio is from about 1:50 to about 1:330.
 18. The method of claim 15in which said o-diazonaphthoquinone derivative is2,4-bis(2-diazo-1,2-dihydro-1-oxo-5-naphthalenesulfonyloxy)benzophenone,2-diazo-1,2-dihydro-1-oxo-5-naphthalenesulfonyloxy-2,2-bis(hydroxyphenyl)propanemonoester, the hexahydroxybenzophenone hexaester of2-diazo-1,2-dihydro-1-oxo-5-naphthalenesulfonic acid,2,2'-bis(2-diazo-1,2-dihydro-1-oxo-5-naphthalenesulfonyloxy)biphenyl,2,2',4,4'-tetrakis(2-diazo-1,2-dihydro-1-oxo-5-naphthalenesulfonyloxy)biphenyl,2,3,4-tris(2-diazo-1,2-dihydro-1-oxo-5-naphthalenesulfonyloxy)-benzophenone,2,4-bis(2-diazo-1,2-dihydro-1-oxo-4-naphthalene-sulfonyloxy)benzophenone,2-diazo-1,2-dihydro-1-oxo-4-naphthalenesulfonyloxy-2,2-bishydroxyphenylpropanemonoester, the hexahydroxybenzophenone hexaester of2-diazo-1,2-dihydro-1-oxo-4-naphthalenesulfonic acid,2,2'-bis(2-diazo-1,2-dihydro-1-oxo-4-naphthalenesulfonyloxy)biphenyl,2,2',4,4'-tetrakis(2-diazo-1,2-dihydro-1-oxo-4-naphthalenesulfonyloxy)biphenyl,or2,3,4-tris(2-diazo-1,2-dihydro-1-oxo-4-naphthalenesulfonyloxy)benzophenone.19. The method of claim 15 in which said infrared radiation absorbingcompound is (i) a squarylium, croconate, cyanine, merocyanine,indolizine, pyrylium or metal dithiolene dye or (ii) a pigment thatabsorbs infrared radiation at a wavelength of from about 800 to about1100 nm.
 20. The method of claim 19 in which component a) is reactionproduct (ii), the phenolic resin is a novolac resin, and theo-diazonaphthoquinone reactive derivative is a sulfonic acid orcarboxylic acid ester of o-diazonaphthoquinone; in which the infraredradiation absorbing compound is present in an amount sufficient toprovide an optical density of at least 0.5; and in which the ratio isfrom about 1:50 to about 1:330.